When you say you've downloaded Maya, you're talking about the Personal Learning Edition right?

I just ask because it is not possible to get a legal download of Maya Complete or Unlimited which could be your problem. It's probably best not to ask for help if you're using dodgy software but if I have grabbed the wrong end of the stick please accept my apologies and if I were you I would get in touch with Autodesk Technical Help...

click for contact phone numbers

hope that helps,

Mat.